Photographic exposure-meter



Oct.'24, 1933. E. BERT-RAM PHOTOGRAPHIG EXPOSURE METR 2 Sheets-Sheet 1Filed Aug. 8, 1930 INVENTOH: By`

Oct. 24, 1933. E. BERTRAM 1,931,883

' PHOTOGRAPHIC EXPOSURE METER Filed Aug. 8, 1930 2 Sheets-Sheet 2Patented Oct. 24, 1933 UNITED STATES PATENT OFFICE AErnst Bertram,Pasing,

near l-Illlnich, Germany Appunti@ uns: s, 19:, senda. 74.023, and inGermany August 20, 1929 Schimi.,

Theinvention relatestoaphotographic exposure-meter which makes a quick.simple and faultlessascertainmentofthetimeof posmble.

According tothe invention a rotary cylinderhavingalongitudinalslotrestsonthemeasuringtube which contains the opticsand on which thel series of times of exposure corresponding totheindividual light valuesarearran'ged. This cylinder is provided with aseries of graduations in proximity to the slot. so that on adiusting a4mark oftherotary cylindertothelight value ascertained, only the seriesof exposure times correspondingtothe said lightnexttotheseriesofgradlmtionawhilstalltheseriesofexposuretimesarehiddenby thecylimier.

The invention is illustratively exemplied in the accompanyingdrawings.inwhich Figure lshows the exposurefmeter in axialsectionandonanenlargedscale,

Fig.2showsoneofthedevicesi'or thelight,

Yliig. 3shows-the tdisc gsinfrontofthedeviccforthelight,

' Flg.4isarontviewoftheent,

liigisaeromsectimofthetube srlandotthecylinderturningonthelattenandFig.6`isadevelopmentoithemeasuringtube 3 The invention consistssubstantially ci a "ioIwhichisenclosedbythetube2Vsmiliesbetweentworings3and4uigularin crosssection.Porthreefourtloftheircireumferencetherinssareprovidedwithanmnberofholes3'. Intheouterrins4thelms-tuhe5is measuringthelight.smallwhite,tsheets'l,in oiisetrelation. Thesheetsar'eallmadeofthe (Gl.iis-z3) v numbers of the light values is always adjacent a sheetV 'I anda hole 3'. The two rings 3 and 4 with the ground glass 1 and thelens-tube 5 hold the light value disc 9 and thesheets 7 together and arearranged in such a manner that the holes 3' register exactly with thelight values 9a and the sheets '7.

On the outer surface of the measuring tube 2 the series 10 of exposuretimes corresponding to the' light values are indicated, as may be seen65 from Fig. 6. On the measuring tube 2 is a rotary cylinder 11 having alongitudinal slot 12 the width and length of which correspond to thewidth and length of the series of number 10. Along the edge of the slot12 a series of gradua- 70 tions 13 is arranged on this cylinder, andthecylinder 11 also carries a table for ascertaining the longest admissibletime of exposure of moved objectsas well as a short direction for use ofthe exposure-meter. These tables and the directions for use are notshown in the drawings for simplicitys sake. As a protection againstatmosphericinfiuences the cylinder l1 is enclosed by a protectivetransparent casing 11. This protective casing is supported by asectional ribbed tube 14,V xed to the tube 1i. in such a manner that theabove mentioned written matter fills out the empty spaces.

0n a ring 15 the same light'values are arranged in the form or a" scalebearing numbers 1-14 85 as on the discof light-values 9. As may be seenfrom Fig; '-6, the spacing of the light value numbers oithering 15corresponds to the spacing o1' the series 10 of exposure times on tube2. 0n the scale-ring 15 there are indicated on 90 l the strip 15' thedegrees of sensitivity of the .plate emulsion expressed in degrees. Therotary scalering 15 'rests on the measuring tube 2 andvis provided withnotches 16 engageable by a nose 11" of a spring-ring 17 fixed to themeasuring 95 tube 2 which prevents inadvertent displacement of thescale-ring 15 after adjustment for the sensitivity of plate emulsion.

As a cover a ilanged socket 18 is introduced in the main tube 2. Restingon the flange o! the socket 18 is theA ground glass 8 enclosed by thelens-tube 5 and kept in position by a nut 19. In the lens-tube 5 a smallcollecting lens 20 is fastened by a ring 21. y

'me magnifying tube 22 receives the narea'cap 105' 23 in which themagnifying lens 24 is fastened. The measuring of the light is-etfectedin the following manner:v

LThescale-ring 151s adiustedbytumingto the degreeot sensitivity oi.' theplate used; this 110 adjustment is complete when the nose 17' of thespring-ring 17 engages the rest 16 corresponding to the degree ofsensitivity.

2. The cap 23 is then placed well into the eye, so that no side-lightenters, and the ring of numbers 9a is adjusted minutely by displacementof the magnifying tube 22. This adjustment should be noted on a scale 25of the tube 22; with all further measuring by the same eye all that isnecessary is to adjust the magnifying tube 22 to the same line-mark ofthe scale 25.

3. Now the object appearing on the blue ground glass 1 is sighted; thenthe series 9a of light values is read up to that number which is clearlylegible without straining the eye; and this number should be noted.

4. Now the cylinder 11 is adjusted with its arrow mark 26 to the samenumberl of the scalering 15 which on measuring has been found to beclearly legible. After this adjustment of the cylinder 11 all the series10 of exposure times are hidden with the exception of that correspondingto the number of light-value adjusted (according to Fig. 4 for instancethe number 13) This series of exposure times is visible through thelongitudinal slot 12 of the cylinder 11. Now, among the series ofgraduations 13 arranged on the cylinder 11 the graduation used fortaking the photo is sought and then there is found at the side the timeof exposure sought.

WhatV I claim is:

1. An exposure meter comprising a tube, a transparent disc in said tubecomprising a plurality of fields of different density, and a centralbore, a second transparent disc contacting with the first disc andcarrying a plurality of characters upon its surface, each thereofregistering with one of the said fields, a second tube provided with amagnifying glass and adjustably connected to said first tube, anexposure time scale attached to the outside of the said first tube, athird tube provided with a slot rotatably mounted upon said rst tube, adiaphragm scale disposed along said slot, a fourth tube rotatablymounted upon the said third tube and carrying a scale with thecharacters provided on the said second disc, and a second scale withvalues of the plate sensitiveness, the proper exposure time being foundby ascertaining the correct field and its character by looking throughthe magnifying glass and then accordingly adjusting the scales byrotation of the several tubes.

2. A device, as claimed in claim 1, in which said first disc consists ofa plurality of white transparent leaves stepwise superimposed to form aplurality of shaded elds, each preceding field having a transparencycorresponding to onehalf of the exposure time which corresponds to thetransparency of the next following eld.

3. An exposure meter, as claimed in claim l, comprising a perforatedring in the said first tube, said perforations registering with thedifferent fields of said rst disc, a ground glass carried by said ring,a second ring member for holding the said two discs and the ground glassupon the first ring, 'a tubular casing centered upon said ground glass,a lens carried by said casing, a support for securing said casing to thetube and a second ground glass surrounding the casing and being attachedto the said support, the lens casing and rst ground glass serving forsighting purposes.

ERNST BERTRAM.

